1. Field of the Invention
The present invention relates to a powder stirring device used in an image forming device, such as a photocopier or a printer.
2. Description of the Related Art
An image forming device, such as a photocopier or a printer, develops images in the following way. First, images are optically read and electrostatic images are formed on the surface of a photosensitive body. Next, powder-type toner is attached to the electrostatic images and is then transferred to a piece of paper. Such a process of developing images is performed in a development unit included in an image forming device.
In general, toner is contained in a toner cartridge under a predetermined pressure to be maintained in a solid state. Powder-type toner can be provided to a development unit after transferring the toner from the toner cartridge to a reserve tank to supply toner and then stir it with a powder stirring device in the reserve tank. An image forming device having such a structure has been disclosed in Japanese Patent Laid-Open Publication No. hei 3-217879. Here, the toner cartridge and the reserve tank may be integrated into one body or may be used separately.
FIG. 1 is a diagram illustrating a conventional image forming device, such as a printer. Referring to FIG. 1, toner contained in a toner cartridge 31 is provided to a reserve tank 32 and stirred therein so that it becomes powdery. Next, the toner is provided from a supply roller 33 of the reserve tank 32 to a development unit 34. The fine-grained toner is attached to electrostatic images formed on a drum of the development unit 34 and is finally transferred to a piece of paper as an image.
In order to regularly attach toner to the electrostatic images formed on the drum of the development unit 34, the amount of the toner needs to be controlled by stirring the toner in the reserve tank 32 with air, in order to reach a powdery state and thus the toner regularly spreads in the direction of the length of the supply roller 33. Accordingly, a powder stirring device to stir toner and convey it in the direction of the length of the supply roller 33 is installed in the reserve tank 32.
FIG. 2 is a diagram illustrating the structure of a conventional reserve tank. Referring to FIG. 2, when grain-type toner is supplied from a toner discharger 42 formed at the lower part of a toner cartridge 41 to a toner supplier 44 formed at the surface of a reserve tank 43, the grain-type toner is mixed with air by two stirring screws 45 and 46 so that it becomes powdery.
The powdery toner is circulated by the two stirring screws 45 and 46 so that it can be repeatedly moved along the direction of the length of the reserve tank 43 and can be regularly spread to the reserve tank 43, as marked by the arrows in FIG. 2. The toner stirred by the stirring screws 45 and 46 is sent to a development unit (not shown) for development. A supply roller 47 is installed near the stirring screw 45 to supply toner to the development unit. The amount of toner in the reserve tank 43 is measured by a toner sensor 48, which includes a piezoelectric vibrator, so that a certain amount of toner required for development can always be saved in the reserve tank 43.
However, in the structure of the conventional powder stirring device, toner cannot be effectively stirred because the toner may attach to the surface of the stirring screws 45 and 46. In particular, in the case of a small-sized image forming device, since the capacities of a reserve tank 43 and the amount of air in the reserve tank 43 are very small, toner may more easily attach to the surface of the stirring screws 45 and 46, and thus it is much more difficult to effectively stir the toner with air. In addition, the stirring screws 45 and 46 have a very complicated structure and are very expensive. It is also very difficult to manufacture the stirring screws 45 and 46 to be compact.
In the case of an image forming device, such as a printer, since the reserve tank 43 has a small capacity, toner in the reserve tank 43 is used up faster, and thus it is necessary to frequently detect how much toner is left in the reserve tank 43. However, a piezoelectric sensor, which is conventionally used as a toner sensor 48, measures the amount of toner based on vibration frequencies that vary depending on the amount of toner attached to the piezoelectric sensor, and thus it is impossible to measure the amount of toner in real time. In other words, a small-sized image forming device, such as a printer, has a small reserve tank and can print images very quickly. However, it is almost impossible to maintain an appropriate amount of toner in the reserve tank 43, unless the amount of toner in the reserve tank is measured often.
Accordingly, it is an aspect of the present invention to provide a powder stirring device which has a simple structure and can effectively stir toner.
It is another aspect of the present invention to provide a powder stirring device which measures the amount of toner left in a reserve tank in real time.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
The foregoing and/or other aspects of the present invention may be achieved by providing a powder stirring device, which stirs toner to be provided to a development unit of an image forming device. The powder stirring device includes a stirring element which is supported in a reserve tank, temporarily storing the toner. The stirring element is arranged away from a rotation axis of the reserve tank or a region adjacent to the rotation axis, so as to be capable of rotating in the reserve tank.
The stirring element may be formed in a bar shape and arranged in parallel with the rotation axis of the reserve tank. The stirring element may be formed in a crank or a spiral shape.
The stirring device may include a pair of bars, which are symmetrically arranged with respect to the rotation axis of the reserve tank and are parallel to the rotation axis of the reserve tank, and ribs, which are formed along the rotation circumference of the pair of bars and are slantingly connected to the pair of bars.
The powder stirring device may further include a unit to detect the amount of toner in the reserve tank. The unit to detect the amount of toner in the reserve tank may be an optical sensor which detects the amount of light passing through a region in the reserve tank where toner is stirred.
The powder stirring device may further include a supply roller which is provided in the vicinity of the stirring element to provide toner to the development unit. The stirring element may be arranged so that its rotation circumference contacts the supply roller.